1. Field of Invention
The present invention relates to a display panel and the like. More particularly, the present invention is directed to enhance low visibility due to the reflection of light incident from the exterior.
2. Description of Related Art
Recently, display devices utilizing a liquid crystal display (LCD), an organic electroluminescent element (hereinafter, “an organic EL element”), and the like are employed in various electronics, such as a cellular phone, a personal computer, an electronic organizer, a portable electronic game console, and the like. As such, users have many opportunities to look at a display screen of the electronic apparatus outdoors as well as looking at the screen indoors.
A related art apparatus, in which light is incident on the display screen from the exterior will now be discussed. The incident light is reflected from the screen back to viewers. However, more intense light is incident on the screen and is reflected from the screen back to the viewers not indoors, but outdoors. As such, the contrast of the display device is reduced, thereby reducing the quality of the display image.
A related art case in which an organic EL element is employed will now be considered. Since the organic EL elements, which are self-luminescent elements, have high visibility and response speed, the display devices employing the organic EL elements are suitable to display moving pictures. However, existing organic EL elements do not simultaneously realize high luminance and a long lifespan. As such, it is impossible to avoid a reduction in visibility due to the effect of light incident from the exterior out of doors. Therefore, in order to enhance contrast, a related art display device has been disclosed in which an antireflection film, composed of a laminated film of TiO2 and SiO2, is formed on the inner and outer surfaces of a cover to seal the display device. See Japanese Unexamined Patent Application Publication No. 2001-230072.
Further, another related art display device has been disclosed in which a circular polarizing plate is formed above a surface of the cover to suppress the reflection of light incident from the exterior See Japanese Unexamined Patent Application Publication No. 8-321381. In addition, a related art structure has been disclosed in which TaOx (tantalum oxide) deposited under a reactive atmosphere or by CVD is used as an absorption layer in order to enhance contrast. See Japanese Patent No. 2901370. Furthermore, an organic EL element, in which a charge injecting layer having light absorption and diffusion properties (see Japanese Patent No. 2931229) is provided, a display panel with a black absorbent formed on the bottom thereof (see U.S. Pat. No. 5,986,401, and an organic EL element, in which a black multi-layered film is used for an electrode (see Japanese Unexamined Patent Application Publication No. 2003-17274) have been disclosed in the related art.
In these related art display devices, since an expensive member, such as a circular polarizing plate, must be provided for a display device, more expense and effort are required, thereby increasing costs. In addition, since a filter, such as a circular polarizing plate, is provided, even though the organic EL element emits light, the light is not emitted externally, thereby lowering actual brightness and thus reducing visibility.
A related art display device has been disclosed in which a triple-layered film of a reflective aluminum film, a silicon oxide/aluminum film, and an aluminum transflective film is used to suppress reflectance. However, in this case, it is not easy to manufacture the display device due to its complicated structure. Further, when the triple-layered film is used as an anode, a separate conductive film having a high work function has to be deposited.